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Fluke 87V & 28II problem at the ohms range .

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Alex:

--- Quote from: Kiriakos-GR on June 27, 2011, 10:05:12 pm ---
--- Quote from: Alex on June 23, 2011, 12:34:05 pm ---Kyriako, did you check the manual of the 28II first? How about you Joshua?

Look at the the resistance specifications on page 48. In the 600 Ohms the resolution claimed is 0.1 Ohms aka 100 mOhm. Also, the accuracy quoted is 2 counts when using the relative function. Despite these specs you are asking it to accurately measure 50mOhms?! If anything, it is exceeding its stated specifications.

http://assets.fluke.com/manuals/2x_2____umeng0100.pdf

Alex

--- End quote ---


High Alex ,  you are correct about the bibliography, but those are the specs for the standard 6000 counts resolution.
At 20.000 counts I do my comparisons.
If I accept the fact the the 87V and the 28II can do measurements from 100mOhm and above,
the conclusion would be that the extra resolution on those DMM's are meaningless.

--- End quote ---

Yeap, thats correct as the manual specifications characterise the limitations/capabilities of the actual measurement hardware, whereas the # of counts should simply reflect that. In this case the firmware should not be displaying digits that have greater error than the digit value. In other words the number of counts is not correct in that range. I'll attribute this to Fluke and rest my case. You are a tough man to convince Kyriako! Pfff  ;D

I haven't seen an audio casette tape for years, not to mention on a bench!   :o
We can tell your are putting the 1272 through its paces; its battery is running low.

Kiriakos-GR:

--- Quote from: Alex on June 29, 2011, 01:27:54 am --- You are a tough man to convince Kyriako! Pfff  ;D
--- End quote ---

Yes I am the crazy one of my village, its true, but I have a talent on finding things,
or at discovering answers when I troubleshoot a problem.

The latest Fluke catalog 2010-2011 called as  11605-eng-01-a.pdf

Check the picture at the bottom.
I would declare my self as totally crazy, if Fluke send a message to me,
saying that the Fluke 28II does not have identical ranges, or resolution with the 87V.


--- Quote from: Alex on June 29, 2011, 01:27:54 am ---I haven't seen an audio casette tape for years, not to mention on a bench!   :o
We can tell your are putting the 1272 through its paces; its battery is running low.

--- End quote ---
On the U1272 I use NiMH on it, so to check the battery life, and I do run battery consumption tests.
But this is a secret.. yet  ;)

Richard W.:
Thats resolution, this means this is the smallest step between to values.

look at this picture: http://www.mw-import.de/images/big/buegelmessschraube-25-50-klassik.jpg
resolution is 0,01mm, but the smallest possible value is 25mm

It's the same with your multimeter.

alm:

--- Quote from: Alex on June 29, 2011, 01:27:54 am ---Yeap, thats correct as the manual specifications characterise the limitations/capabilities of the actual measurement hardware, whereas the # of counts should simply reflect that. In this case the firmware should not be displaying digits that have greater error than the digit value.

--- End quote ---
Less resolution than accuracy is bad, about one digit more resolution is optimal (to reduce quantization error), more is not very useful from accuracy point of view, but may be useful for relative measurements (as long as the linearity is good enough). I believe we've discussed this issue somewhat recently. The extra resolution doesn't hurt, it just doesn't give you extra accuracy. It's up to the user to be aware of the accuracy specifications and calculate the measurement error. It's rare for a meter to be accurate down to the last digit.

Alex:
On-screen quantisation error (we dont know whats going on inside) will be limited to half a least significant digit, i.e. 50mOhms for the 28II in the 600 Ohm range. We must also consider the 'counts' error which is 2 counts i.e. 200mOhm for the 28II in the 600Ohm range. If the multimeter had an extra digit (600.00 Ohms) then the counts specification would be wrong as the resolution would refer to the second decimal from the right and the count to the last decimal point.

So for the 28II, 600.0 Ohms range with an input of 0.1Ohms, according to the manual we have ±(0.2 % + 2) using the REL function ofc:
±(((0.1*0.2)/100)+0.2) Ohms = 0.1 Ohms ± 0.2002 almost equal to 0.1 Ohms ± 0.2 Ohms. For higher resistances the %of error drops off quickly as you would expect.

I would not use this DMM for accurate measurements below say 10 Ohms. The Fluke 289 (50000 counts) has a 50 Ohm range with 1milliOhm resolution, 0.15 % + 20 counts accuracy error. Even that is pushing it.

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